MAX1221 Datasheet, PDF (24/44 Pages) Maxim Integrated Products – 12-Bit, Multichannel ADCs/DACs with FIFO, Temperature Sensing, and GPIO Ports

12-Bit, Multichannel ADCs/DACs with FIFO,
Temperature Sensing, and GPIO Ports
Channels 8–11 are invalid. Any scans or averages on
these channles can cause corrupt data.
Select scan mode 00 or 01 to return one result per sin-
gle-ended channel and one result per differential pair
within the selected scanning range (set by bits 2 and 1,
SCAN1 and SCAN0), plus one temperature result if
selected. Select scan mode 10 to scan a single input
channel numerous times, depending on NSCAN1 and
NSCAN0 in the ADC averaging register (Table 9).
Select scan mode 11 to return only one result from a
single channel.
Setup Register
Issue a command byte to the setup register to config-
ure the clock, reference, power-down modes, and ADC
single-ended/differential modes. Table 5 details the bits
in the setup-register command byte. Bits 5 and 4
(CKSEL1 and CKSEL0) control the clock mode, acqui-
sition and sampling, and the conversion start. Bits 3
and 2 (REFSEL1 and REFSEL0) set the device for either
internal or external reference. Bits 1 and 0 (DIFFSEL1
and DIFFSEL0) address the ADC unipolar-mode and
bipolar-mode registers and configure the analog input
channels for differential operation.
The ADC reference is always on if any of the following
conditions are true:
1) The FBGON bit is set to one in the reset register.
2) At least one DAC output is powered up and
REFSEL[1:0] (in the setup register) = 00.
3) At least one DAC is powered down through the
100kΩ to V_REF and REFSEL[1:0] = 00.
If any of the above conditions exist, the ADC reference is
always on, but there is a 188 clock-cycle delay before
temperature-sensor measurements begin, if requested.
Table 4. Conversion Register*
BIT
NAME
—
BIT
FUNCTION
7 (MSB) Set to one to select conversion register.
CHSEL3
Analog input channel select
6
(MAX1223). Set to 0 on the
MAX1221/MAX1343.
CHSEL2
CHSEL1
CHSEL0
SCAN1
SCAN0
5
Analog input channel select.
4
Analog input channel select.
3
Analog input channel select.
2
Scan mode select.
1
Scan mode select.
TEMP
0 (LSB)
Set to one to take a single temperature
measurement. The first conversion
result of a scan contains temperature
information.
*See below for bit details.
CHSEL3 CHSEL2 CHSEL1 CHSEL0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
0
1
0
1
0
1
1
0
0
1
1
1
1
0
0
0
1
0
0
1
1
0
1
0
1
0
1
1
SELECTED
CHANNEL (N)
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AIN8
AIN9
AIN10
AIN11
SCAN1 SCAN0
0
0
0
1
1
0
1
1
SCAN MODE
(CHANNEL N IS SELECTED BY
BITS CHSEL3–CHSEL0)
Scans channels 0 through N.
Scans channels N through the highest
numbered channel.
Scans channel N repeatedly. The ADC
averaging register sets the number of
results.
No scan. Converts channel N once only.
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